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United States Patent |
6,191,674
|
Adachi
,   et al.
|
February 20, 2001
|
Ignition coil for internal combustion engine
Abstract
An ignition coil that can be easily assembled, that assures co-axial
alignment of a primary coil, a secondary coil and a center core part, and
that generates desired high voltage. A core body is formed to have an
outer diameter larger than that of a permanent magnet so that the
permanent magnet will not protrude out of the outer peripheral face of the
core body. Accordingly, when the center core part is inserted into a
secondary spool, the center core part is not caught by the secondary spool
and may be readily inserted and assembled therewith. Also, because no
bulge is created at the center core part, it is possible to prevent the
center core part from tilting within the secondary spool and to readily
assure the co-axial alignment of the primary spool, the secondary spool
and the center core part. Thus, voltage generated by the secondary coil is
prevented from dropping, and high voltage may be applied to the ignition
plug.
Inventors:
|
Adachi; Norihiro (Kariya, JP);
Shimoide; Yoshihiro (Tokai, JP);
Osuka; Kazutoyo (Gamagori, JP);
Kawai; Kazuhide (Kariya, JP)
|
Assignee:
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Denso Corporation (JP)
|
Appl. No.:
|
456546 |
Filed:
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December 8, 1999 |
Foreign Application Priority Data
| Dec 14, 1998[JP] | 10-354084 |
Current U.S. Class: |
336/90; 123/634; 336/92; 336/96 |
Intern'l Class: |
H01F 027/02; F02P 011/00 |
Field of Search: |
336/90,96,92
123/634,635
|
References Cited
U.S. Patent Documents
5703556 | Dec., 1997 | Kikuta et al. | 336/83.
|
5870012 | Feb., 1999 | Sakamaki et al. | 336/107.
|
Foreign Patent Documents |
8-93616 | Apr., 1996 | JP.
| |
9-115749 | May., 1997 | JP.
| |
9-246071 | Sep., 1997 | JP.
| |
10-223464 | Aug., 1998 | JP.
| |
11-74139 | Mar., 1999 | JP.
| |
Primary Examiner: Gellner; Michael L.
Assistant Examiner: Mai; Anh
Attorney, Agent or Firm: Nixon & Vanderhye PC
Claims
What is claimed is:
1. A high-voltage internal combustion engine ignition coil, comprising:
a center core part having a core body and a permanent magnet disposed at at
least one end of the core body; and
a cushion member covering an outer surface of the core body and the
permanent magnet so that the permanent magnet is disposed within an outer
periphery of the cushion member, wherein an angle .theta. between a bottom
surface of the core body and an imaginary straight line A between a bottom
edge of the core body and a top edge of the permanent magnet satisfies a
condition of 45.degree..ltoreq..theta..ltoreq.90.degree..
2. The ignition coil of claim 1, wherein an outer diameter of the permanent
magnet is smaller than an outer diameter of the core body.
3. The ignition coil of claim 1, wherein the core body comprises a
plurality of laminated steel plates.
4. The ignition coil of claim 1, wherein the cushion member has a
shrink-fit temperature higher than a coil environment use temperature.
5. The ignition coil of claim 4, wherein the shrink-fit temperature is
greater than or equal to 150.degree.0 C.
6. The ignition coil of claim 1, further comprising primary and secondary
coils disposed in radial relation to one another around the center core
part.
7. The ignition coil of claim 1, further comprising a housing member for
housing the ignition coil and being filled with a resin insulating
material.
8. A high-voltage internal combustion engine ignition coil, comprising:
a center core part having a core body and a first cushion member disposed
at at least one end of the core body; and
a second cushion member covering an outer surface of the core body and said
first cushion member so that said first cushion member is disposed within
an outer periphery of the second cushion member;
wherein an outer diameter of the first cushion member is smaller than an
outer diameter of the core body, and wherein the second cushion member has
a shrink-fit temperature higher than a coil environment use temperature.
9. The ignition coil of claim 8, wherein the core body comprises a
plurality of laminated steel plates.
10. The ignition coil of claim 8, wherein an angle .theta. between a bottom
surface X of the core body and an imaginary straight line A connecting a
bottom edge of the core body and a top edge of the first cushion member
satisfies a condition of 45.degree..ltoreq..theta..ltoreq.90.degree..
11. The ignition coil of claim 8, wherein the first cushion member is
formed from hard rubber.
12. The ignition coil of claim 8, wherein the shrink-fit temperature is
greater than or equal to 150.degree. C.
13. The ignition coil of claim 8, further comprising primary and secondary
coils disposed in radial relation to one another around the center core
part.
14. The ignition coil of claim 8, further comprising a housing member for
housing the ignition coil and being filled with a resin insulating
material.
15. An engine ignition coil, comprising:
a metal core;
one of a magnet and a cushion member having a width less than that of the
metal core and disposed at one end of the metal core;
a thermo-contractive tube shrink-fitted around the metal core and the one
of the magnet and the cushion member to maintain the one of the magnet and
the cushion member in alignment with the metal core.
16. The ignition coil of claim 15, wherein the thermo-contractive tube has
a shrink-fit temperature higher than a coil environment use temperature.
17. The ignition coil of claim 16, wherein the shrink-fit temperature is
greater than or equal to 150.degree. C.
18. A high-voltage internal combustion engine ignition coil, comprising:
a center core part having a core body and a permanent magnet disposed at at
least one end of the core body; and
a cushion member covering an outer surface of the core body and the
permanent magnet so that the permanent magnet is disposed within an outer
periphery of the cushion member,
wherein the cushion member has a shrink-fit temperature higher than a coil
enviroment use temperature.
19. The ignition coil of claim 18, wherein the shrink-fit temperature is
greater than or equal to 150.degree. C.
Description
CROSS-REFERENCE TO RELATED APPLICATION
The present application is related to, and claims priority from, Japanese
Patent Application No. Hei. 10-354084, the contents of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ignition coil for an internal
combustion engine, and more specifically to a stick-type ignition coil
directly mounted in an ignition plug hole.
2. Description of the Related Art
One type of conventional stick-type ignition coil for an internal
combustion engine includes a center core part having an axially-disposed
rod-like core body. A resin spool around which a primary coil and a
secondary coil are wound is disposed around the center core part, and
resin is filled within a coil housing to insulate the first coil from the
second coil. The resin filled within the housing not only acts as an
insulator but also prevents the coils from becoming loose, as the resin
flows between adjacent wire rods of the coils before hardening.
Another type of conventional ignition coil includes a center core formed by
disposing a permanent magnet having almost the same outer diameter as the
core body outer diameter at both axial ends of the core body to increase
the amount of voltage generated by the ignition coil. Alternatively, an
ignition coil may include a rubber cushion member instead of the
above-described permanent magnet to reduce axially-directed force acting
on the core body due to different expansion coefficients of the respective
members to prevent magnetostriction of the core body.
However, as shown for example in FIG. 6, because the core body and the
permanent magnet or the cushion member are formed to have almost the same
outer diameter, a bulge 82 is created at the interface 94 between the core
body 93 and the permanent magnet 95 or the cushion member composing the
center core part 92 unless the core body and the permanent magnet or the
cushion member are co-axially assembled. Further, because cracks or voids
in the insulation will occur where the center core part 92 expands and
contacts, along with the resin insulating member and casing members having
different expansion coefficients, due to temperature fluctuation, the
center core part 92 is covered by a thermo-contractive tube 97 as a
resin-made elastic cushion member, for example, to prevent the cracks from
occurring.
However, because the thermo-contractive tube 97 also covers the outside of
the bulge 82, the thermo-contractive tube 97 also causes a bulge 97a.
Therefore, assembly time is increased because the spool tends to catch on
the bulge 97a during assembly of the center core part 92 into the spool of
the secondary coil. Further, it is difficult to assure co-axial alignment
of the primary coil, the secondary coil and the center core part 92
because the center core part 92 tends to tilt within the spool. As a
result, voltage generated by the secondary coil is decreased, and desired
high voltage cannot be applied to the ignition plug.
Further, because the thermo-contractive tube 97 is inhibited from shrinking
uniformly due to the deformation in the vicinity of the bulge 97a, the end
97b of the thermo-contractive tube 97 comes off as shown in FIG. 6, the
center core part 92 covered by the thermo-contractive tube 97 becomes
larger than its predetermined size and the center core part 92 cannot be
assembled at the predetermined position within the secondary spool, and
the thermo-contractive tube 97 is damaged by a bulge 93b of the center
core 93 opposite the bulge 97a.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide an ignition coil
that can be easily assembled, that can assure co-axial alignment of a
primary coil, a secondary coil and a center core part, and that can
generate desired high voltage.
Another object of the invention is to provide an ignition coil that
prevents cracks from occurring in the axial vicinity of both end corners
of the center core and that generates desired high voltage.
Accordingly, the present invention provides a core body including an outer
diameter larger than the outer diameter of a permanent magnet or a cushion
member installed at an axial end of the core body, so that the permanent
magnet or cushion member may be easily assembled to the core body within
the range of the outer diameter of the core body. Consequently, it is
possible to prevent the permanent magnet or cushion member from deviating
and protruding radially away from the core body.
Further, it is possible to prevent the center core part from being caught
within a secondary spool or from tilting within the secondary spool when
the core body is assembled with the permanent magnet or cushion member in
the secondary spool. Accordingly, the center core part may be readily
inserted into the secondary spool. Also, the primary spool, the secondary
spool and the center core part may be co-axially aligned, therefore making
it possible for desired high voltage to be applied to the ignition plug.
More specifically, the center core part is preferably covered by an elastic
cushion member at axial ends of the core body so that casing members
surrounding the center core part and the resin insulating member are
prevented from directly contacting both axial ends of the center core
part.
Also, cracks in the resin insulating material and the casing member near
the axial ends of the center core part are prevented, even when the resin
insulating material and the casing member have expansion coefficients
different from that of the center core part, and expand and contract
repeatedly together with the center core part due to temperature changes.
Cracks are prevented because the elastic cushion member absorbs the
difference in the expansion coefficients of the center core part, the
resin insulating material and the casing member. Therefore, voltage
generated by the secondary coil is prevented from dropping, and desired
high voltage can subsequently be applied to the ignition plug.
Further, the contraction temperature of the thermo-contractive casing
member may be made higher than the ambient temperature to prevent
expansion damage in the thermo-contractive casing member during coil
operation.
The specific nature of the invention, as well as other objects, uses and
advantages thereof, will clearly appear from the following description and
from the accompanying drawings in which like numerals refer to like parts.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional view showing an ignition plug according to a
preferred embodiment of the present invention;
FIG. 2 is an enlarged partial sectional view of the ignition plug shown in
FIG. 1;
FIG. 3 is a sectional view showing a center core section and a
thermo-contractive casing member of the ignition plug of the present
invention;
FIG. 4 is a diagram showing the positional relationship between the core
member and a permanent magnet of the ignition plug of the present
invention;
FIG. 5 is a partial sectional view of the ignition plug of the present
invention; and
FIG. 6 is a sectional view of a prior art ignition plug.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIGS. 1 and 2, an ignition coil 10 is mounted in an ignition
plug hole for each cylinder in an engine block (not shown), and is
electrically connected to an ignition plug (not shown) also mounted within
the plug hole. The ignition coil 10 includes a cylindrical resin housing
11 that defines a storage chamber 11a. A center core part 12, a secondary
spool 20, a secondary coil 21, a primary spool 23, a primary coil 24, an
outer peripheral core 25 and the like are stored in the storage chamber
11a. The center core part 12 is composed of a core body 13 and permanent
magnets 14, 15 disposed on both sides of the core body 13. Epoxy resin 26
fills in gaps between the respective members within the ignition coil 10.
The resin, which is an insulating material, assures electrical insulation
among the members.
The cylindrical core body 13 is formed from thin silicon steel plates
laminated together in the radial direction so that its resulting cross
section is almost circular. The permanent magnets 14, 15 have polarities
that are opposite from the direction of generated magnetic flux generated
when the magnets are excited by the coil. A thermo-contractive tube, or
casing member, 17 covers the core body 13 and acts as an elastic cushion
member at the outer periphery thereof. A cap 19 having a through hole is
fitted over the permanent magnet 14 covered by the thermo-contractive tube
17. The cap 19 and the secondary spool 20 compose a casing member
surrounding the outer periphery of the center core part 12.
Because the thermo-contractive tube 17 is molded into a cylindrical shape
and its inner diameter at the time of molding is larger than the outer
diameter of the center core part 12, it is possible to insert the center
core part 12 in which the permanent magnets 14, 15 are assembled with the
core body 13 into the thermo-contractive tube 17. The thermo-contractive
tube 17 in which the center core part 12 is inserted shrinks when heated
as discussed later and adheres to the center core part 12, except at the
location of a concavity 81 formed in the vicinity of the interface between
the core body 13 and the permanent magnet 15.
As shown in FIG. 3, the thermo-contractive tube 17 has a cylindrical part
17a, ringed parts 17b, 17c provided at both axial ends of the cylindrical
part 17a, and first and second edges 17d, 17e located between the
cylindrical part 17a and the ringed parts 17b, 17c, respectively. The
cylindrical part 17a covers the peripheral side face of the center core
part 12, the ringed parts 17b, 17c respectively cover part of both axial
end faces of the center core part 12, the first edge 17d covers the end
edges of the permanent magnets 14, 15 at both ends of the center core part
12, and the second edge 17e covers both end edges of the core body 13.
Preferably, the thermo-contractive tube 17 shrinks at temperatures higher
than typical environment usage temperatures (-30.degree. to 150.degree.
C.) and the epoxy resin setting temperatures (up to 150.degree. C.) during
coil production. This is so because, when the thermo-contractive tube 17
has a damaged section, the damaged section expands due to the shrinkage,
and the thermo-contractive tube 17 is therefore not as effective as an
elastic cushion member if the shrinkage temperature is lower than the use
environment temperature. It is therefore possible to prevent the damaged
section from expanding by setting the shrinkage temperature to be higher
than the use environment temperature and the manufacturing temperature.
As shown in FIG. 1, the secondary spool 20 is a molded resin cylinder
disposed around the thermo-contractive tube 17 and closed at the end of
the permanent magnet 15. The secondary coil 21 is wound around the
secondary spool 20, and a dummy coil 22 is also wound around the secondary
spool 20 on the high voltage side. The dummy coil 22 electrically connects
the secondary coil 21 with a terminal plate 40. The surface area of the
dummy coil is increased to avoid an electric field from concentrating at
the dummy coil 22.
The primary spool 23 is also formed from a molded resin and is disposed
around the secondary coil 21. The primary coil 24 is wound around the
primary spool 23. A switching circuit (not shown) for supplying a control
signal to the primary coil 24 is provided on the outside of the ignition
coil 10 and is electrically connected with the primary coil 24 via a
terminal that is insert-molded to a connector 30.
The peripheral core 25 is mounted further around the primary coil 24, and
is formed by a cylindrically wound thin silicon steel plate. The core 25
has an axial gap, as the beginning of the winding is not connected with
the end thereof, and extends from the permanent magnet 14 to the permanent
magnet 15.
A high-pressure terminal 41 is insert-molded under the housing 11. The
center part of the terminal plate 40 is a claw section bent in the
direction in which the high-pressure terminal 41 is inserted to
electrically connect the high-pressure terminal 41 with the terminal plate
40. A wire rod at the high voltage end of the dummy coil 22 is
electrically connected to the terminal plate 40 by fusing, soldering or
the like. A spring 42 is electrically connected to the high-pressure
terminal 41 and with the ignition plug when the ignition coil 10 is
inserted to the plug hole. A rubber plug cap 43 is attached to the opening
end on the high voltage side of the housing 11, and the ignition plug is
inserted into the plug cap. When a control signal is supplied from the
switching circuit to the primary coil 24, high voltage is generated in the
secondary coil 21 and is applied to the ignition plug via the dummy coil
22, the terminal plate 40, the high-pressure terminal 41 and the spring
42.
Next, referring to FIG. 4, the relationship between the outer diameter of
the center core part 12 and the outer diameter of the permanent magnets
14, 15 will be explained.
The core body 13 has a diameter D.sub.1 larger than the diameter D.sub.2 of
the permanent magnet 15. The diameter D.sub.2 of the permanent magnet 15
is set so as to satisfy the following conditions. When the permanent
magnet 15 is assembled with the center core part 12, and when the angle
between the radial direction X of the core body 13 and a straight line A
connecting an edge 13a of the core body 13 and an edge 15a of the
permanent magnet 15 is .theta., .theta. is preferably between
45.degree..ltoreq..theta..ltoreq.90.degree.. That is, when the distance
from a peripheral face 13b of the core body 13 to a peripheral face 15b of
the permanent magnet 15 is d and the axial length of the permanent magnet
15 is t, preferably d.ltoreq.t.
Although .theta. may be less than 45.degree. if the permanent magnet 15 is
capable of enhancing the generated voltage, the thermo-contractive tube 17
may be damaged by the edge 13a of the core body 13 if .theta. is too
small. Meanwhile, if 90.degree.<.theta., the permanent magnet 15 protrudes
out of the core body 13, and a bulge 83 is formed as shown in FIG. 6.
Because the core body 13 has an outer diameter which is larger than the
outer diameter of the core body 13 as shown in FIG. 1, a concavity 81 is
formed around the permanent magnet 15. Therefore, the permanent magnet 15
will not protrude out of the peripheral face 13b of the core body 13 when
it is co-axially assembled with the core body 13. Further, even when the
permanent magnet 15 cannot be co-axially assembled with the core body 13,
the permanent magnet 15 will not protrude and may be disposed in diametric
alignment with the core body 13 readily within the range of the outer
diameter of the core body 13 as long as the degree of deviation is as
shown in FIG. 5.
Also, because the thermo-contractive tube 17 may be prevented from being
deformed at the time of shrinkage and the end of the thermo-contractive
tube 17 may be prevented from being peeled off from the end face of the
permanent magnet 15, the center core part 12 may be maintained with the
above-mentioned predetermined shape. Accordingly, the center core part 12
may be assembled in the predetermined position to prevent the
thermo-contractive tube 17 from being damaged.
In addition, because no bulge is formed on the center core part 12, the
center core part 12 is prevented from tilting within the secondary spool
20, thereby ensuring co-axial alignment of the primary spool 23, the
secondary spool 20 and the center core part 12. As a result, it is
possible to prevent the voltage generated by the secondary spool 20 from
dropping, and it is possible to apply the desired high voltage to the
ignition plug.
Therefore, according to the present invention, because no bulge is created
on the center core part 12, the thermo-contractive tube 17 is prevented
from being damaged in the vicinity of the interface between the core body
13 and the permanent magnet 15 when the thermo-contractive tube 17
shrinks. Further, according to the present invention, it is possible to
prevent the peripheral side face of the center core part 12 and the end
edge of the permanent magnets 14, 15 from directly contacting the
secondary spool 20 and the epoxy resin 26 by covering the peripheral side
face of the center core part 12 and the end edge of the permanent magnets
14, 15 with the thermo-contractive tube 17. Also, the thermo-contractive
tube 17 can deform elastically during temperature changes to absorb the
difference in component expansion coefficients even when the center core
part 12, the secondary spool 20 and the epoxy resin 26 having different
expansion coefficients.
Accordingly, because it is possible to prevent cracks from occurring around
the peripheral side face of the center core part 12 and in the secondary
spool 20 and the epoxy resin 26 around both end corners of the center core
part 12 where cracks are particularly liable to occur, it is possible to
prevent discharge from occurring between the high voltage section and the
center core part 12. Therefore, desired high voltage may be applied to the
ignition plug.
In addition, according to the present invention, even when the core body 13
and the permanent magnet 15 composing the center core part 12 cannot be
co-axially assembled, a certain degree of deviation shown in FIG. 5 is
permissible. Accordingly, the use of a cylindrical guide member having the
inner diameter of the center core part 12 allows the core body 13 and the
permanent magnet 15 to be automatically assembled.
Although the permanent magnets 14, 15 have been disposed on both ends of
the core body 13 in the embodiment described above, a permanent magnet may
be disposed only at one end of the core body 13. Further, it is possible
to dispose a cushion member formed of hard rubber or the like at one or
both ends of the core body 13 instead of the permanent magnet. This
arrangement would prevent magnetostriction caused by an axially-directed
force relative to the core body 13 due to the difference of expansion
coefficients that would otherwise decrease the permeability of the core
body 13.
Alternatively, a laminate member in which the permanent magnet or the
cushion member are laminated may be disposed at the end of the permanent
magnet as an independent member. In this case, it is possible to prevent
damage to the elastic cushion member and the occurrence of cracks and
magnetostriction in the same manner as described above by setting the
outer diameter of the cushion member to be smaller than the outer diameter
of the permanent magnet.
Still more, although the thermo-contractive tube has been applied as the
elastic cushion member in the embodiment described above, elastic members
such as elastomer resin and rubber may be alternatively utilized.
While the preferred embodiment has been described, variations thereto will
occur to those skilled in the art within the scope of the inventive
concepts delineated by the following claims.
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